There are numerous applications in the electrohydraulic control field in which it is desired to control motion at an actuator system and load. In a die casting machine, for example, it is desirable closely to control the profile of motion at the so-called shot cylinder that pushes molten metal into the machine die cavity. Specifically, velocity of the shot cylinder ram must be closely controlled as a function of ram position to obtain optimum machine efficiency and throughput, while maintaining product quality and reducing material waste through die separation and flashing, etc. Wear at the cylinder and die cavity are also reduced, and machine productivity therefore is increased, when both velocity and stroke of the shot cylinder ram can be closely controlled and tailored to die cavity volume and configuration.
It is therefore a general object of the present invention to provide an electrohydraulic actuator system that obtains enhanced and precise control of motion at the actuator and load. Another object of the present invention is to provide a system of the described character that embodies state-of-the-art electronic control capability, and yet is easy and economical to implement both in new system construction and in retrofit of existing systems.
A further and more specific object of the present invention is to provide an electrohydraulic system for controlling velocity at an actuator load, such as the shot cylinder of a die casting machine, as a precise yet programmable function of position. A related object of the invention is to provide a shot cylinder control system for a die casting machine that includes a facility for programming and storing a plurality of operator-selectable velocity versus position control profiles, for adjustment of impact force at the end of the ram stroke for reducing die separation and flashing at the machine, and/or for graphic display of desired and/or actual velocity profile at the hydraulic cylinder and ram. Yet another object of the invention is to provide a shot cylinder control system of the described character that employs PC-compatible or other conventional hardware familiar to the operator, and user-friendly state-of-the-art control programming that is easy to employ and yet features enhanced control precision and versatility.